1. Field of the Invention
The present invention relates to new copolymers and use of such copolymers as a resin binder component for photoresist compositions, particularly chemically-amplified positive-acting resists. Polymers of the invention include 1) photoacid-labile groups, 2) meta-hydroxphenyl groups, and 3) para-hydroxyphenyl groups.
2. Background
Photoresists are photosensitive films used for the transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. In general, photoresist compositions comprise at least a resin binder component and a photoactive agent.
More recently, chemically-amplified-type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain xe2x80x9cblockingxe2x80x9d groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar fictional group is formed, e.g., carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al., Proceedings of SPIE, 2724:334-343 (1996); and P. Trefonas et al. Proceedings of the 11th International Conference on Photopolymers (Soc. Of Plastics Engineers), pp 44-58 (Oct. 6, 1997).
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance, applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
The present invention provides novel copolymers and photoresist compositions that comprise a photoactive component and such copolymers as a resin binder component. The copolymers of the invention in general comprise at least one repeating unit that is a meta-hydroxyphenyl derivative, at least one repeating unit that is a para-hydroxyphenyl derivative and one or more photoacid-labile groups.
We have found that resists that contain a resin of the invention can exhibit excellent properties thereby enabling formation of highly resolved resist images. Resists that have too high of a dissolution rate can exhibit relatively decreased resolution, particularly when printing micron or sub-micron features. It has been particularly found that addition of a meta-hydroxyphenyl unit to a polymer containing para-hydroxy and acid labile units can quite favorably impact solubility differentials between exposed and unexposed regions of a resist coating layer that contains the polymer.
Particular preferred copolymers of the invention include units provided by polymerization of a meta-hydroxy vinylphenyl compound (such as meta-hydroxy styrene or meta-hydroxy a-methylstyrene), para-hydroxystyrene (such as para-hydroxy styrene or para-hydroxy xcex1-methylstyrene) and an acrylate ester to provide photoacid-labile groups. Polymers of the invention also may contain other units, such as optionally phenyl groups (e.g. as may be provided by copolymerization of a styrene compound), cyano (as may be provided by provided by copolymerization of acrylonitrile), etc.
The invention also provides method for forming relief images, including methods for forming a highly resolved relief image such as a pattern of lines where each line has essentially vertical sidewalls and a line width of about 0.40 microns of less, or even about 0.25 microns or less. The invention further provides articles of manufacture comprising substrates such as a microelectronic wafer or a liquid crystal display or other flat panel display substrate having coated thereon the photoresists and relief images of the invention.
Unless otherwise indicated, the term xe2x80x9ccopolymerxe2x80x9d refers herein to polymers other than homopolymers, and thus includes terpolymers, tetrapolymers, etc. Additionally, references herein to xe2x80x9cmeta-hydroxyphenylxe2x80x9d groups or xe2x80x9cparahydroxyphenylxe2x80x9d groups or other similar terms are inclusive of groups that may have phenyl ring substituents in addition to a hydroxy group at the specified position. Generally preferred meta-hydroxyphenyl groups of copolymers of the invention do not have hydroxy substitution at the para position, and more preferably only have a single hydroxy substitution at a meta position. Generally preferred para-hydroxyphenyl groups of copolymers of the invention do not have hydroxy substitution at a meta position, and more preferably only have a single hydroxy substitution at the para position.
Other aspects of the invention are disclosed infra.